Debugging Node.js Applications Quiz Quiz

Challenge your understanding of debugging Node.js applications, focusing on common practices, tools, and error handling strategies important for effective back-end development workflows. This quiz will help you assess and expand your proficiency in troubleshooting Node.js code, identifying bugs, and optimizing applications.

1. Identifying Synchronous vs. Asynchronous Errors

   When debugging Node.js code, which type of error is most commonly missed if only focusing on synchronous code paths, as in the following example with a file reading callback?

   1. Array out-of-bounds error
   2. Asynchronous error
   3. Compilation error
   4. Typo in function name

   Explanation: Asynchronous errors often occur in callbacks or promises and are missed if your attention is only on synchronous operations. While typos and out-of-bounds errors can cause bugs, they are typically easier to spot through static analysis. Compilation errors are generally identified before code is run, as Node.js is interpreted. The key issue is that asynchronous errors do not manifest until after event loop execution, requiring different debugging strategies.

2. Using the Debugger Statement

   What happens when Node.js code execution reaches a 'debugger;' statement while the process is started with debugging enabled?

   1. Execution pauses, allowing inspection
   2. An error is thrown and execution stops
   3. Console.log is automatically called
   4. The line is ignored

   Explanation: When Node.js is run with debugging enabled, reaching a 'debugger;' statement causes execution to pause, giving developers a chance to inspect variables and step through code. If the line were ignored, it would not help with debugging. Throwing an error would unnecessarily disrupt the process. The 'debugger;' statement does not trigger a console log; it only affects the execution flow for inspection.

3. Handling Uncaught Exceptions

   In Node.js, which event should you listen to in order to capture unhandled errors that cause the process to crash, as in the case of an unhandled exception in asynchronous code?

   1. exceptionThrown
   2. uncaughtException
   3. errorCaught
   4. unhandledPromiseReject

   Explanation: Listening to the 'uncaughtException' event allows you to catch errors not handled elsewhere, preventing immediate process termination. 'errorCaught' and 'exceptionThrown' are not valid event names and will not be triggered for such issues. 'unhandledPromiseReject' is for unhandled promise rejections, which is related but not equivalent to uncaught synchronous exceptions.

4. Using Built-in Debugging Tools

   Which Node.js command-line flag should you use to start a script with built-in debugging capabilities, allowing you to set breakpoints and inspect execution?

   1. --inspect
   2. --trace
   3. --debbug
   4. --debugg

   Explanation: --inspect is the standard flag that enables debugging, allowing tools to connect for interactive inspection. Flags like --debbug and --debugg are common typos and will not be recognized. --trace provides stack traces but does not enable a debugging interface. Choosing the right flag is essential for accessing built-in debugging tools.

5. Locating a Memory Leak

   If a Node.js application exhibits steadily rising memory usage without releasing memory, which tool or technique is most effective for identifying the source of the leak?

   1. Heap snapshot
   2. Syntax linter
   3. Module bundler
   4. Semantic versioning

   Explanation: A heap snapshot allows inspection of memory usage, helping to pinpoint objects that are not being released and likely causing leaks. A syntax linter only checks for stylistic or minor syntactic issues, not runtime memory problems. A module bundler is for packaging code, unrelated to debugging memory usage. Semantic versioning is for version control, not debugging. The heap snapshot is the most direct solution for diagnosing such issues.